MDA5 cleavage by the Leader protease of foot-and-mouth disease virus reveals its pleiotropic effect against the host antiviral response

Abstract

The RIG-I-like receptor (RLR) melanoma differentiation-associated gene 5 (MDA5) plays a key role in triggering innate antiviral response during infection by RNA viruses. MDA5 activation leads to transcription induction of type-I interferon (IFN) and proinflammatory cytokines. MDA5 has also been associated with autoimmune and autoinflammatory diseases by dysfunctional activation of innate immune response in the absence of infection. Here, we show how footand-mouth disease virus (FMDV) counteracts the specific antiviral effect exerted by MDA5 targeting the protein for cleavage by the viral Leader protease (Lpro). MDA5 overexpression had an inhibitory effect on FMDV infection in IFNcompetent cells. Remarkably, immunostimulatory viral RNA co-immunoprecipitated with MDA5 in infected cells. Moreover, specific cleavage of MDA5 by Lpro was detected in co-transfected cells, as well as during the course of FMDV infection. A significant reduction in IFN induction associated with MDA5 cleavage was detected by comparison with a non-cleavable MDA5 mutant protein with preserved antiviral activity. The Lpro cleavage site in MDA5 was identified as the RGRAR sequence in the conserved helicase motif VI, coinciding with that recently reported for Lpro in LGP2, another member of the RLRs family involved in antiviral defenses. Interestingly, specific mutations within the MDA5 Lpro target sequence have been associated with immune disease in mice and humans. Our results reveal a pleiotropic strategy for immune evasion based on a viral protease targeting phylogenetically conserved domains of immune sensors. Identification of viral strategies aimed to disrupt MDA5 functionality may also contribute to develop new treatment tools for MDA5-related disorders.

Foot-and-Mouth Disease Virus Evades Innate Immune Response by 3C-Targeting of MDA5

“…Although a previous study showed that MDA5 overexpression showed more significant antiviral activity than RIG-I overexpression against FMDV [ 24 ], it dealt with the interplay between 2B and RIG-I only. Another study reported that L pro cleaved exogenous MDA5 but it did not show any evidence of degradation of endogenous MDA5 [ 38 ].…”

“…Lb is more abundant than Lab in infected cells [ 42 ] and is associated with translocation to the nucleus and cleavage of NF-kB and IRF3/7 proteins [ 43 , 44 , 45 ]. Since the direct interaction between the FMDV Lb pro and MDA5 has recently been reported [ 38 ], we focused on the interplay between FMDV 3C pro and MDA5, which has not been elucidated at all.…”

Picornaviruses: A View from 3A

“…A direct role for 3A in evading the cellular innate antiviral responses within infectedcells remains to be clarified and this activity will need to be combined with understanding of the role of viral proteases in antagonizing the cellular antiviral response [185,186,322], and with the global reductions in cellular transcription [82] and translation [323] that occur in picornavirus-infected cells. Each of these processes contributes significantly to the downregulation of cellular innate immunity.…”

“…It would be of interest to determine if 3A interacts with RIG-1, MDA5 and MAVS in FMDV-infected cells derived from a natural host of FMDV. Moreover, the above observations need to be reconciled with similar studies that concluded that expression of FMDV 3A (or 3AB) does not influence expression of ISGs in HeLa cells following treatment with IFNβ [193], and more recent studies which showed that L pro targets MDA5 for degradation in FMDV-infected porcine cells [186].…”

“…To combat the cellular antiviral response, picornaviruses have evolved a number of strategies. These include: inhibition of host-cell protein synthesis and transcription, preventing nuclear translocation of transcription factors, or inducing degradation (either indirectly by proteasome-and caspase-dependent processes, or directly via virus-encoded proteases) of host proteins that sense infection [82,[184][185][186][187]. HAV 3A has been implicated as having an indirect role in evading antiviral responses.…”